Trityl resins are useful solid phase bonded protecting groups, originally developed for solid phase peptide synthesis and as well used for solid phase organic synthesis. Solid phase bonded 2-chlorotrityl chloride (2-CTC resin) is commercial available [CBL Patras] and based on crosslinked polystyrene (Ps) or modified polystyrenes (e. g. tentagel, polystyrene grafted with polyethyleneglycol) [1: catalog ACT, Noviabiochem]. The 2-CTC linker is an acid labile resin and because of its excellence properties playing a significant role in novel linker technology [2: THL 1997, 6347, 2629; Int. J. Pep. Prot. Res. 37 (1991) 513]. Cleavage of peptides from 2-CTC resin can be effected by treatment under very mild acidic conditions (e. g. dilute TFA/DCM, AcOH/DCM, HFIP) [1, 3: Liebigs A. 1988, 1079, THL 1997, 7299]. Despite being an expensive and a valuable synthetic tool, a simple, efficient, gentle, reproducible experimental description for the recycling of—in solid phase synthesis—“used 2-CTC resin” without any loss of activity is so far unknown in the literature.
To synthesize 2-CTC resin from the 2-chlorotriphenylcarbinol resin (2-CT-OH resin), references are given to the experimental procedure of the parent tritylchloride resin from the triphenylmethanol resin in an analogous manner [4: THL 1989, 3943; Can. J. Chem. 54 (1976) 926] or more detailed [1, 5: THL 1998, 3241; 6: React. Funct. Polym. 41 (1999) 111].

WO 01/85758 A2 [7] discloses the recycling of carboxylic acid (e.g. preferably trifluoroacedic acid) trityl ester resins with HCl in CH2Cl2. Apart of the fact that trifluoroacedic acid trityl esters are subject to hydrolysis [8: Z. Phy. Chem. 113 (1978) 199] and therefore difficult to handle, the reexamination of the example given in [7] achieved only 77% of the content of active chloride [6] before use.

After loading of 2-CTC resin with Fmoc-amino acids, unreacted active sites are end-capped with alcohols, especially methanol and Fmoc protecting groups are deprotected with amines, especially piperidine [1, 9: W. C. Chan, P. D. White in Fmoc Solid Phase Peptide Synthesis] leading to a certain amount of methylether and amine substructures in the resin. These substructures decrease the yield of the recycling step and consequently the activity (content of active chloride) of the recycled resin.